Various machines and apparatus have rotational support portions in which rolling bearings such as ball bearings, roller bearings or tapered roller bearings are installed. Such rolling bearings have seal devices installed therein, so that grease filled in the interior of the rolling bearings is prevented from leaking out or various kinds of foreign matter such as rain water or dust on the outside are kept from entering the interior of the rolling bearings.
FIGS. 1 to 3 show three examples of conventional seal devices installed in the opening portion at one end of a rolling bearing for the purposes mentioned above.
FIG. 1 shows a first example of the conventional seal device structures as disclosed in Japanese Patent Publication Tokuko Hei2-52140, which comprises a radially outer seal ring 3 and a radially inner seal ring 4 in combination. This seal device is mounted between an outer ring 8 and an inner ring 11, portions of which are illustrated in FIG. 1. The rotational center of the outer and inner rings 8, 11 is located on the lower side of the inner ring 11 in FIG. 1. The radially outer seal ring 3 comprises a reinforcing metal member 1a and a seal member 2a, and the radially inner seal ring 4 comprises a reinforcing metal member 1b and a seal member 2b, In this structure, the seal member 2a of the seal ring 4 is formed with one or two seal lips having a tip end edge placed in sliding contact with a surface portion of the reinforcing metal member 1a of the mating seal ring 3, while the seal member 2b of the seal ring 3 is formed with one or two seal lips having a tip end edge placed in sliding contact with a surface portion of the reinforcing metal 1b of the mating seal ring 4.
FIG. 2 shows a second example of the conventional seal device structures as disclosed in Japanese Utility Model Publication JitsuKaiHei 2-146221, which comprises a reinforcing metal member 5, a slinger 6 and seal member 7. This seal device is mounted between an outer ring 8 and an inner ring 11, portions of which are illustrated in FIG. 2. The rotational center of the outer and inner rings 8, 11 is located on the lower side of the inner ring 11 in FIG. 2.
The seal member 5 is formed in an annular shape with a L shaped cross section, and comprises a radially outer cylindrical portion 9 and a radially inner ring portion 10. The radially outer cylindrical portion 9 is adapted to be fitted into and fixed to the inner peripheral portion at one end of the outer ring 8, and the radially inner ring portion 10 extends radially inwards from the axially inner end edge of the cylindrical portion 9. The term "axially inner end edge" is used to mean the end edge closer to the axially central portion of the rolling bearing (the left end edge in FIG. 2).
The slinger 6 is formed in an annular shape with an L shaped cross section, and comprises a radially inner cylindrical portion 12 and a radially outer ring portion 13. The radially inner cylindrical portion 12 is adapted to be fitted onto and fixed to the outer peripheral portion at one end of the inner ring 11, and the radially outer.,, ring portion 13 extends radially outwards from the anally outer end edge of the cylindrical portion 12. The term "axially outer end edge" is used to mean the end edge closer to the axial opening portion of the rolling bearing (the right end edge in FIG. 2).
The seal member 7 is made of an elastic material such as rubber or elastomer and has a base portion 7a and three seal lips, i.e. outer seal lip 14, intermediate seal lip 15 and inner seal lip 16. The base portion 7a is securely connected to the reinforcing metal 5.
The outermost seal lip 14 has a tip end edge placed in sliding contact with an axially inner surface portion of the ring portion 13 of the slinger 6 and the remaining seal lips, i.e intermediate seal lip 15 and inner seal lip 16, have tip end edges placed in sliding contact with the outer peripheral surface portion of the cylindrical portion 12 of the slinger 6.
FIG. 3 shows a third example of the conventional seal device structures as disclosed in Japanese Utility Model Publication JitsuKaiHei 3-121224, which is formed in a structure similar to that of the second example in FIG. 2, except that the innermost seal lip 16 of the three seal lips of the seal member 7 is tilted in a direction opposite to that of the second example, with its tip end edge closer to the axial central portion of the rolling bearing.
The three examples mentioned above are still required to be improved in some points as follows;
In the example of FIG. 1, the radially outer and inner seal rings 3, 4 comprising the reinforcing metal members 1a, 1b and the seal members 2a, 2b, are troublesome in manufacturing so as to increase the cost of the whole seal device.
In the example of FIG. 2, the tip end edge of the inner seal lip 16 is inclined to be separated from the outer peripheral surface of the cylindrical portion 12 of the slinger 6 before installing the seal device to the open end portion of the rolling bearing or before installing the rolling bearing with the seal device to a rotational support portion.
Once the tip end edge of the seal lip 16 is separated from the outer peripheral surface of the cylindrical portion 12 of the slinger 6, the inner seal lip 16 often turns over when the tip end edge of the seal lip 16 is fitted onto the outer peripheral surface of the cylindrical portion 12 of the slinger 6 by relatively axially moving the reinforcing metal member 5 and slinger 6 closer to each other. In the turned-over state, the contact pressure between the tip end edge of the seal lip 16 aid the outer peripheral surface of the cylindrical portion 12 of the slinger 6 is excessively large, so that the rotational torque, that is rotational resistance in the rolling bearing with the seal device installed therein, becomes large and the seal performance becomes instable.
In order to avoid such problems, the axial length of the cylindrical portion 12 may be enlarged, or the tip end edge of the inner seal lip 16 can be made closer to the ring portion 13 of the slinger 6 to increase the axial length between the tip end edge of the inner seal lip 16 and the axially inner end edge of the cylindrical portion 12 of the slinger 6. However, if the axial length of the cylindrical portion 12 is enlarged, the installation space of the seal device will sometimes become intolerably large. And, if the tip end edge of the inner seal lip 16 is made closer to the ring portion 13 of the slinger 6, the distance between the tip end edge of the seal lip 16 and the tip end edge of the intermediate seal lip 15 is too short to cause interference therebetween so as to worsen the seal performance.
In the example of FIG. 3, even if the tip end edge of the seal lip 16 is separated from the outer peripheral surface of the cylindrical portion, 12 of the slinger 6, the inner seal lip 16 never turns over when the tip end edge of the seal lip 16 is fitted onto the outer peripheral surface of the cylindrical portion 12 of the slinger 6. However, when the performance of the inner seal lip 16 for preventing grease leakage is too perfect, grease hardly reaches the sliding contact portions between the intermediate and outer seal lips 15, 16 and the slinger 6. Accordingly, the wear at the sliding contact portions can become large and the seal performance can be worsened at the sliding contact portions.
In addition, when the root portion 16a of the inner seal lip 16 and the root portion 15a of the intermediate seal lip 15, connected to the base portion 7a, are close to each other, the seal performance is worsened due to the interference between the inner and intermediate seal lips 16, 15.